By using a coordinated multipoint transmission/reception (CoMP for short) technology, multiple network devices can share channel state information and user data information, to perform joint multipoint transmission or reception, so as to implement effective utilization of network resources. However, all existing CoMP technologies are based on an ideal backhaul, and the ideal backhaul means that information may be exchanged between different network devices at a low delay and at a high throughput rate. The network device herein may be a base station, a remote radio head, or the like.
In an actual scenario, because of a factor such as an environment or different manufacturers, it is quite difficult to implement an ideal backhaul. For example, for multiple network devices, there may be an ideal backhaul between some network devices, for example, an ideal backhaul between multiple RRHs controlled by one base station; however, there may also be a non-ideal backhaul between some other network devices.
In an ideal backhaul case, a dynamic point selection technology or a dynamic point blanking technology (dynamic point selection or dynamic point blanking) may be used, so that some network devices may be selected to transmit data to user equipment on some time-frequency resources in a subframe, and other network devices may not transmit data on these time-frequency resources.
In a communications system, a hybrid automatic repeat request (HARQ) technology may be used. In the HARQ technology, a network device transmits data in one data block to user equipment, and if the user equipment correctly receives the data, the user equipment feeds back a positive acknowledgement (ACK for short), or if the user equipment does not correctly receive the data, the user equipment feeds back a negative acknowledgement (NACK for short). If the network device receives the NACK, the network device performs retransmission of the data block, or if the network device receives the ACK, the network device transmits a new data block.
Regardless of initial transmission or retransmission of a data block, in an ideal backhaul case, network devices may quickly share information such as a channel state, or transmitted or received data; therefore, in a case in which data sent by a network device is not correctly received by UE, the network device may dynamically select another network device for data retransmission. Therefore, switching between multiple network devices may be dynamically performed for initial transmission and retransmission in an HARQ process, so as to obtain a multipoint coordination gain.
In a non-ideal backhaul scenario, there is a relatively large delay for information exchange between multiple network devices; therefore, a network device is likely fail to learn a data sending status of another network device in a timely manner, for example, fails to learn whether data sent by another network device is correctly received by UE. Therefore, a dynamic retransmission solution in an ideal backhaul scenario cannot be used, and in the non-ideal backhaul scenario, a coordination gain cannot be obtained by means of coordination between multiple network devices in an aspect of data transmission.
For a same network device, the network device may perform coordination in an aspect of data transmission by means of quick information exchange between multiple modules in the network device, so that a coordination gain is obtained. However, the solution to implementing quick information exchange between multiple modules is relatively complex.